Conversion of hydrocarbon oils



J. M. BARRON CONVERSION OF HYDROCARBON OILS Sept )13, 938

Filed Ap ril 7 JOSEPH M. BARRoN INVENTOR i ATToRNEY Patented Sept. 13, 1938 TAT '1.'.

yCNVEJRSIN F HYDROCARBQN OILS `l'oseph M. Barron, Port Arthur, Tex., assigner to 'lihe Texas Company, New York, N. Y., a corporation of Delaware Application April 7, w37, Serial No. 135,377 Y Claims.

rI'his invention relates to conversion of hydrocarbon oils and has to do particularly with the cracking of hydrocarbon oils to lower boiling products, such as gasoline, in a cracking operation involving the principle of gas reversion.

in the cracking of higher boiling oils to lower boiling products, it has been found advantageous to carry out the cracking of the heavier oils in the presence of normally gaseous hydrocarbons. Une source of suchnorrnally gaseous hydrocarbons is the gases evolved in the cracking operation. In order to recover the normally gaseous hydrocarbons evolved in the cracking process, it is advantageous to use a scrubbing medium which r may conveniently be charging stock to the system. rThis charging stockenriched with the normally gaseous hydrocarbons may then be charged to the cracking zone wherein the higher boiling oil undergoes cracking in the presence of gaseous hydrocarbons. During the cracking operation the normally gaseous hydrocarbons enter into the conversion reactions to produce increased amounts of the desired low boiling liquid hydrocarbons.

In accordance with the present invention, the iced stock enriched with the gaseous hydrocarbons may be charged to the heating and cracking zone and preferably the gaseous hydrocarbons are separated from the enriched feed stock and the gaseous hydrocarbons so separated charged to an intermediate point in the cracking zone.

More particularly, according to the invention, it is preferred to employ a cracking operation in which the cracking is carried out in zones of heating and soaking. A feature of the present invention is mixing an oil enriched with the gaseous hydrocarbons recovered from the cracking system with a condensate recycle stock and the hashing from this mixture the normally gaseous hydrocarbon fraction which is returned to the soaking zone of the cracking system.

lThe invention will be more fully understood from the following description taken in connection with the accompanying drawing which shows in elevation asketch ofone form of apparatus for carrying out the process.

In the following description an apparatus is described for carrying out the process in which a tion may be applied to any well known type of l cracking operation, for example one operating on a recycle basis in which the cracking is carried (Cl. 15m-9) out in cracking and soaking zones, such as coil and drum.

Referring to the drawing, numeral l represents the cracking furnace, 2, 3 and a series of soaking drums, a primary fractionator, 6 a second- 5 ary fractionator, l a naphtha stabilizer and t a gas absorber. The furnace is shown as a vertical, circular type and the soaking drums as a series of vertical stills. It is to be understood, however, that any well known type of furnace may lo be used and one, or more than one, reaction drum may be employed. The furnace contains two coils, lil and l2, for cracking the clean oil and dirty oil respectively. It is intended that the invention shall not be limited to a two-coil lo cracking system but instead a single coil may be used, for example as in semi-clean or super-y clean circulation; the semi-clean in which the recycle stock and charge are cracked in the same coil; the super-clean in which the distillate re- 2o cycle stock is cracked in a separate coil and then combined with the dirty recycle stock or mixture of charge and dirty recycle stock and sent to a soaking or coking zone. lin any of these types of operation the recycle stock may be combined 25 with the rich oil containing normally gaseous hydrocarbons, preferably recovered from the system, the mixture flashed and the normally gaseous hydrocarbons introduced into the soaking zone.

ln practicing the invention with the apparatus shown, the charging stock, such as gas oil, crude oil, naphtha, crude residuum etc., is introduced through the line i5 and forced by the pump i@ through the line il to a heat exchange coil it, located in a reflux condenser section i d, superimposed on the secondary fractionator t. A, portion or all oi the charge may be by-passed through the line E@ and conducted through the line 2i to the top of the absorber d as a scrub- 4o hing medium. c v

In some cases it may be desirable to use a second oil, such as a special gas oil or naphtha, as an absorbent or scrubbing medium, and in this case such an oil would be introduced through the e5 line 23 and forced by the pump 2li through the line 2i to the absorber 8 by suitable regulation of the Valve 25 in the line 2i and the valve to in the line 2l. A portion of this oil may be sent directly through the line di to the heat exchange so coil id.

rihe gases introduced into the absorber d are principally butane and lighter and may be derived from the stabilizer l oraccumulator 3U, .both of which communicate with the absorber 8 through the lines 3| and 32 respectively. These gases are scrubbed countercurrently with the oil introduced through the line 2l andthe desired gases absorbed in the scrubbing medium while the unabsorbed or iixed gases are released from the top of the absorber through the line 34. It is intended that the Cs and C4 hydrocarbons and a portion of the C2 hydrocarbons, if desired, may be absorbed. The rich oil is withdrawn from the bottom of the absorber through the line 35 in which is located a pump 36, and combined with the remainder of the charge in the line I1, if any, and the mixture conducted to the heat exchange coil I8, where they pass in indirect heat exchange with the cracked vapors from the system.

The oil is conducted from the coil I8 through the line 40 to another heat exchange coil 4I, located in the lower portion of the fractionator 6. 'I he preheated oil is transferred from the coil 4I through the line 42 to a flash drum 44. In the coil I8 the oil is preheated to a temperature of about 3D0-325 F. and further heated in the coil 4I to a temperature of 15G-500 F. There is also drawn into the flash drum 44 a dirty cracking or recycle stock from theeprimary fractionator 5 through the line 45, in which is located a pump 46. 'Ihe latter oil may be at a temperature of about 830-860 F. The ash drum is maintained under relatively high pressure which may be 400- 600 pounds per square inch or higher. The pressure may be regulated by the valve 41 in the line 48. It is preferable' to regulate the pressure to around 420-450 pounds per square inch and at this pressure gases are released 'through the valve 41 and passed through the line 48 to the entrance of the soaking drum 2. The unvaporized oil in the flash drum 44 is withdrawn from the bottom thereof through the line 58 in which is located a pump 5I. Any proportion of this oil may be introduced into theupper portion of the fractionator 5 as a dephlegmating medium through the branch line 52 controlled by valve 53. 'Ihe remainder of the charge is conducted through the line 54 to the dirty oil crackingcoil 2. The temperature of this oil entering the coil I2 is usually around 750800 F. In the coil i2 the oil is raised to a temperature of about S30-890 F. and then discharged into the line 56 leading to the soaking drum 2.

A clean recycle stock is withdrawn from the bottom of fractionator 6 through the line 60 and forced by the pump 6i to the clean oil heating coil I0. A portion of the clean recycle stock may be withdrawn from the line 60 through the bypass line 62, cooled in the cooling coil 63 and the cooled product by-passed through the line 64 to the upper portion of the fractionator 5 as a reflux medium. The recycle stock is heated to a temperature. of about S50-1000* F. and then mixed with the hot products from the residuum heating coil I2. The mixture at a temperature of about SOO-910 F. is then passed through the line 58 wherein it is mixed with gases from the line 48 and the mixture introduced into the top of the soaking drum 2. The products pass serially through the soaking drums which are connected by lines 66 and 61. About 30G-600 pounds pressure, or more, may be maintained on the reaction drums and preferably around 400 pounds pressure. The temperature in the reaction drums may vary considerably but a satisfactory temperature mayl be about 900 F. on soaking drum 2, about 885 Ff' on soaking drum 3 and about 870 F. on soaking drum 4. Liquid products collect in the bottom of soaking drum 4 and these liquids are continuously withdrawn so as to maintain a low liquid level in this drum. The liquid products so withdrawn are discharged through the line 69 by automatic control valve 16 and discharged from the system or further treated, as desired, for example in a tar stripper.

'Ihe vapors are withdrawn from the drum 4 through the line 12 to the fractionator 5. In the fractionator 5 a heavy condensate is pro duced and collects with the reflux mediums introduced through lines 52 and 64 to form a mixture of dirty oil which is Withdrawn from the bottom of the fractionator 5 vthrough the line 45 and forced by the pump 46 into a flash drum 44, the operation of which has been described above. The vapors from the' fractionator 5 are withdrawn through the line 14, and conducted to the lower portion of the secondary fractionator 6. In the fractionator 6, substantially all the hydrocarbons of higher boiling point than the desired nal distillate are condensed and collected in the lower portion of the fractionator as a clean distillate recycle stock which is withdrawn from the bottom of the fractionator through the line 60, as described heretofore.

In order to obtain adequate separation of the vapors, a reiiux condenser I9 is shown superimposed upon the secondary Iractionator 6. The vapors from fractionator 6 pass from the upper portion of the fracticnator 6 through the vapor line 15 to the reiux condenser, wherein additional reiiux condensate forms and ows from the reflux condenser through the line 16 into the top of the fractionator 6. The vapors containing the motor fuel hydrocarbons are withdrawn from the top of the reiiux condenser through the vapor line 18, condensed in the condenser 19 and the condensate collected in the accumulator 30. The accumulator 30 may be maintained under about -200 pounds pressure and uncondensed vapors and gases are released through the valve controlled line 32 and conducted to the absorber 8, the operation of which has been described heretofore.

The condensate in the accumulator 30 is withdrawn through the liquid draw-off line 8I and introduced into the lower portion of the stabilizer 1. In the stabilizer the undesired normally gaseous hydrocarbons are stripped from the distillate. The liquid collecting in the bottom of the stabilizer comprises stabilized naphtha which is drawn from the bottom of the stabilizer through the line 82. The normally gaseous hydrocarbons, including Ca and C4 hydrocarbons, are conducted from the top of the stabilizer through the line e 3I to the lower portion of the absorber 8.

In practicing the invention charging a crude residuum, and recycling about 35% by weight of C3 and C4 hydrocarbons, a 7% increase in naphtha yield may be obtained.

The present invention provides a convenient means of obtaining the benets of gas reversion without substantial loss in fresh charge capacity and no materially increased tendency toward coke formation in the heating coil.

Obviously many modifications and variations of the invention, as hereinbefore set forth, may

be made without departing from the spirit and scope thereof and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim:

i. A process for the conversion of hydrocarbons to produce motor-fuel, which comprises subjecting a higher boiling hydrocarbon oil to cracking conditions of temperature and pressure whereby lower boiling hydrocarbons are formed, passing the cracked products to a so-aking zone to undergo further conversion, separating the cracked products into vapors and residuum, fractionating the vapors to separate therefrom a fraction containing insuiiiciently 'cracked hydrocarbons, passing said insumciently cracked hydrocarbons to a flashing zone, also introducing into said ashing zone charging stock containing normally gaseous hydrocarbons, separating in the flash zone a vapor fraction containing said normally gaseous hydrocarbons, passing 'said vapor fraction to the soaking zone and charging the residual fraction from the ashing zone to the cracking operation.

2, A process for the conversion of hydrocarbons to produce motor fuel, which comprises subjecting a hydrocarbon oil to conversion temperatures in zones of heating and soaking, separating the cracked products into vapors and a residual oil, dephlegmating the vapors to form a reflux condensate and an uncondensed vapor fraction, transferring the reux condensate to a ashing zone, fractionating the uncondensed vapor fraction to separate the motor fuel from normally gaseous hydrocarbons, absorbing the higher boiling portion of said normally gaseous hydrocarbons in a hydrocarbon oil, introducing said hydrocarbon oil and absorbed gaseous hydrocarbons into said hashing zone, separating in said flashing zone normally gaseous hydrocarbons, passing said normally gaseous hydrocarbons so separated to the soaking zone and charging oil from the flashing zone to the cracking zone.

3. A process for. conversion of higher boiling hydrocarbon oils into lower boiling hydrocarbon oils, vcomprising subjecting the oil tocracking temperatures in zones of heating and soaking, separating the cracked products into vapors and a residual oil, fractionating the vapors to form a dirty cracking stock, a clean recycle stock, a motor fuel condensate and normally gaseous hydrocarbons, returning the clean recycle stock to said heating zone, scrubbing the normally gaseous hydrocarbons with a lean absorbent oil to absorb the higher boiling constituents of said normally gaseous hydrocarbons, combining the resultant rich absorbent oil with said dirty cracking stock, flashing from the resulting mixture a fraction containing normally gaseous hydrocarbons, introducing said fraction containing normally gaseous hydrocarbons into said soaking zone, subjecting the bottoms from the flashing operation to cracking temperatures and introducing the cracked product into said soaking zone.

4. A process for the conversion of hydrocarbons to produce motor fuel, which comprises subjecting hydrocarbon oils to a conversion operation whereby motor fuel hydrocarbons are formed, separating the products of reaction into vapors and residuum, fractionating the vapors to separate a reflux condensate, commingling said reux condensate and fresh charge containing normally gaseous hydrocarbons, flashing said mixture to form residual oil and a fraction containing normally gaseous hydrocarbons, charging said residual oil to the conversion operation and introducing said fraction containing normally gaseous hydrocarbons into the conversion operation at an intermediate point thereof.

5. A process for the conversion of hydrocarbons to produce motor fuel, which comprises subjecting hydrocarbon oils to a conversion operation whereby motor fuel hydrocarbons are formed, separating the products of reaction into vapors and residuum, fractionating the vapors to produce a recycle stock and an imstabilized motor fuel, subjecting said unstabilized motor fuel to stabilization thereby forming a stabilized motor fuel and normally gaseous hydrocarbons, contacting said normally gaseous hydrocarbons with a cracking stock thereby absorbing higher boiling constituents of the normally gaseous hydrocarbons, preheating the resultant enriched cracking stock with the aid of heat from said recycle stock, ashing the preheated product to form a volatile fraction containing normally gaseous hydrocarbons and a residual oil, charging said recycle stock and residual oil to said conversion operation and introducing said volatile fraction containing normally gaseous hydrocarbons into the conversion operation at an intermediate point thereof.

6. A process for the treatment of hydrocarbons which comprises preheating' a charging stock containing normally gaseous hydrocarbons, flashing the preheated mixture to produce a volatile fraction containing normally gaseous hydrocarbons and a residual oil, subjecting said residual oil to a conversion operation in zones of heating and soaking to form motor fuel products, passing said volatile fraction containing normally gaseous hydrocarbons to said soaking zone, separating from the reaction products a recycle stock, subjecting said recycle stock tocracking temperatures, and introducing the hot products into the soaking zone.

'1. A process for the treatment of hydrocarbons which comprises scrubbing residual gases from the conversion of hydrocarbon oils with a cracking stock thereby enriching'the cracking stock with normally gaseous hydrocarbons, separating the enriched cracking stock into a volatile fraction containing normally gaseous hydrocarbons and residual oil, subjecting the residual oil to conversion in zones of heating and soaking, charging said volatile fraction to the soaking zone, separating from the products of reaction a recycle stock, a motor fuel fraction and residual gases, heating the recycle stock to cracking temperatures, passing the hot products to the soaking zone, and conducting the residual gases to the rst mentioned scrubbing operation.

JOSEPH M. BARRON. 

